The aim of this project is to investigate attention related processes in schizophrenia with the help of event-related brain potential (ERP) measures. Specifically, it is intended to explore possible cognitive aspects of the sensory-gating phenomenon that was reported to be impaired in schizophrenics, some of their relatives, and active affective disordered patients. The modifiability of the auditory P50 response in schizophrenic and control patients will be examined using two Conditioning-testing paradigms: (l) the basic sensory-gating paradigm, and (2) a procedure manipulating the level of processing demands regarding the testing stimulus and the mere presentation (yes/no) of the conditioning (warning) stimulus. The sensory-gating phenomenon is hypothesized to reflect the overlapping effects of cognition-insensitive proactive inhibition and an attention regulation process triggered by the warning stimulus, with the inhibiting or enhancing effects depending on the processing demands imposed on the subject in regard to the testing stimulus. The schizophrenics, suspected to be impaired in the second (cognitively mediated) but not in the first process, are expected to demonstrate a steady level of suppression of the P50 response to the testing stimulus, unmodified by cognitive manipulation. Supporting results will put schizophrenic stimulation flooding hypothesis in a wider information processing context.